Fluorescent hybridization probes have developed into an important tool in the sequence-specific detection of DNA and RNA. The signals generated by the appended fluorescent labels (or dyes) can be monitored in real time and provide simple, rapid, and robust methods for the detection of biological targets and events. Utility has been seen in applications ranging from microarrays and real time PCR to fluorescence in situ hybridization (FISH).
Recent work in the area of multichromophores, particularly regarding conjugated polymers (CPs) has highlighted the potential these materials have in significantly improving the detection sensitivity of such methods (Liu and Bazan, Chem. Mater., 2004). The light harvesting structures of these materials can be made water soluble and adapted to amplify the fluorescent output of various probe labels (See U.S. patent application Ser. No. 10/600,286, filed Jun. 20, 2003 and Gaylord, Heeger, and Bazan, Proc. Natl. Acad. Sci., 2002, both of which are incorporated herein by reference in their entirety).
In particular, cationic CPs have shown strong affinity for oppositely charged nucleic acids, ensuring the distances required to transfer energy from a photo-excited polymer (a light harvesting donor) to a fluorescently labeled probe/target pair. The light output can be increased by 75-fold relative to the directly excited dye alone (Liu and Bazan, J. Am. Chem. Soc., 2005). The signal amplification adds a variety of benefits in both homogeneous and heterogeneous detection formats.
Results such as these indicate CPs to be highly promising in the field of nucleic acid diagnostics, particularly where sample quantities are scarce. However, there exist methods for the amplification (or replication) of nucleic acid targets, i.e., PCR. Comparatively, in the field of protein recognition, there are no such simple methods for amplifying the targeted materials. As such, signal enhancement arising from CP application is of high consequence in this area.
Dye-labeled antibodies are regularly used for the detection of protein targets in applications such as immunohistochemistry, protein arrays, ELISA tests, and flow cytometry. Integrating CP materials into such methodologies promise to provide a dramatic boost in the performance of such assays, enabling detection levels previously unattainable with conventional dyes.